// -*- coding: utf-8 -*-
// Copyright (C) 2015, 2018 Laboratoire de Recherche et Développement
// de l'Epita (LRDE)
// Copyright (C) 2004, 2005  Laboratoire d'Informatique de Paris 6 (LIP6),
// département Systèmes Répartis Coopératifs (SRC), Université Pierre
// et Marie Curie.
//
// This file is part of Spot, a model checking library.
//
// Spot is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
//
// Spot is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
// License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

#pragma once

#include <cstddef>
#include <type_traits>

/// \defgroup hash_funcs Hashing functions
/// \ingroup misc_tools

/// \ingroup hash_funcs
/// @{

/// \brief Thomas Wang's 32 bit hash function.
///
/// Hash an integer amongst the integers.
/// http://web.archive.org/web/2011/concentric.net/~Ttwang/tech/inthash.htm
inline size_t
wang32_hash(size_t key)
{
	// We assume that size_t has at least 32bits.
	key += ~(key << 15);
	key ^= (key >> 10);
	key += (key << 3);
	key ^= (key >> 6);
	key += ~(key << 11);
	key ^= (key >> 16);
	return key;
}

/// \brief Knuth's Multiplicative hash function.
///
/// This function is suitable for hashing values whose
/// high order bits do not vary much (ex. addresses of
/// memory objects).  Prefer spot::wang32_hash() otherwise.
/// http://web.archive.org/web/2011/concentric.net/~Ttwang/tech/addrhash.htm
inline size_t
knuth32_hash(size_t key)
{
	// 2654435761 is the golden ratio of 2^32.  The right shift of 3
	// bits assumes that all objects are aligned on a 8 byte boundary.
	return (key >> 3) * 2654435761U;
}

/// Struct for Fowler-Noll-Vo parameters
template<class T, class Enable = void>
struct fnv
{};

/// Fowler-Noll-Vo hash parameters for 32 bits
template<class T>
struct fnv<T, typename std::enable_if<sizeof(T) == 4>::type>
{
	static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value,
				  "Fowler-Noll-Vo hash requires an unsigned integral type");
	static constexpr T init = 2166136261UL;
	static constexpr T prime = 16777619UL;
};

/// Fowler-Noll-Vo hash parameters for 64 bits
template<class T>
struct fnv<T, typename std::enable_if<sizeof(T) == 8>::type>
{
	static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value,
				  "Fowler-Noll-Vo hash requires an unsigned integral type");
	static constexpr T init = 14695981039346656037ULL;
	static constexpr T prime = 1099511628211ULL;
};

/// \brief Fowler-Noll-Vo hash function
///
/// This function is a non-cryptographic fast hash function.
/// The magic constants depend on the size of a size_t.
template<class It>
size_t
fnv_hash(It begin, It end)
{
	size_t res = fnv<size_t>::init;
	for (; begin != end; ++begin) {
		res ^= *begin;
		res *= fnv<size_t>::prime;
	}
	return res;
}
/// @}
